Production of ammonium nitrate-fuel oil blasting agents which when deto-nated resultin gaseous mixtures of low toxity



United States PatentOfiFice 7 3,129,128 Patented Apr. 14, 1964PRODUCTION OF AMMONIUM NITRATE-FUEL OIL BLASTING AGENTS WHICH WHEN DETO-NATED RESULT IN GASEOUS NHXTURES F LOW TOXITY Henrylr S. Berczely,Orrautia del Mar, Lima, Peru, assignor to Explosives S.A., Pisco, Lima,Peru, a corporation of Peru No Drawing. Filed July 31, 1962, Ser. No.213,585

4 Claims. (Cl. 149-46) This invention relates to the production ofmixtures of ammonium nitrate and fuel oil which when detonated result ingaseous mixtures which are of low toxicity, and non-toxic to humans, andmore particularly to the process of producing such mixtures involving asimple and readily applicable control to insure proper proportionment ofthe ammonium nitrate and the fuel oil, so that, when the resultantmixture is detonated, the gaseous products produced are of low toxicityand not toxic to humans.

Mixtures of 94.0% to 94.5% of ammonium nitrate and 5.5% to 6% suitablepetroleum oils, usually No. (Class) 2 diesel fuel oil, called Akremiteor ANFO, have been recommended recently for underground blasting, usingconventional dynamites for the detonation of the mixture.

One of the basic conditions for the use of explosives in undergroundblasting operations is that the fumes of the explosions should have aminimum quantity of toxic gases and should not be toxic to humans, thusavoiding fatal accidents. Conventional explosives made with anitroglycerine base are closely controlled by the manufacturers toobtain this result. The investigations of the US. Bureau of Mines,published in the Symposium of the Missouri School of Mines andMetallurgy in 1959, have shown that the toxicity of the fumes resultingfrom the explosion of the ANFO mixture depends on the relativeproportions of the ammonium nitrate and fuel oil. According to theseinvestigations the quantity and composition of the fumes or gaseousatmosphere produced by the explosion is not markedly different from thequantity and composition of the fumes produced in the explosion of thecommercial dynamites, when the content of the fuel oil in the ANFO isstrictly maintained between 5.5% and 6%, the detonation properly madeand there is no excessive humidity in the mixture. Reducing thepercentage of fuel oil in the mixture below 5.5 results in a highquantity of extremely toxic nitrogen dioxide (NO or N 0 in the fumes ofthe explosion.

According to Bulletin 272 of 1941 of the United States Public HealthService, nitrogen dioxide is about 40 times more toxic than carbonmonoxide. Since the densityv of nitrogen dioxide is higher than that ofair, a longer time is required to dissipate nitrogen dioxide bydiffusion 1 than is required for carbon monoxide, whose density is equalto air.

The Conference of the Governmental Industrial Hygienists of the UnitedStates established in 1954 that the maximum amount of allowableconcentration of nitrogen dioxide for an 8-hour exposure is 5 partsnitrogen dioxide per million parts of air. Higher concentrations in theair may cause severe lung irritations, the symptoms of which are delayedfor several hours, even for several days. In comparison, carbon monoxidecan be tolerated for an 8-hour exposure in a concentration of 100 partsof CO per million parts. It is also known that a concentration greaterthan 200 parts of nitrogen dioxide per million causes incurable illness,and that 0.025% (250 ppm.) in the air is the lethal limit. According toBulletin 272 of the United States Public Health Service, until 1941,accidents in the industry caused 107 deaths due tical conditions.

to nitrogen dioxide, a statistic which does not include the number ofnon-fatal accidents.

My investigation has shown that ammonium nitrate fuel oil mixturescontaining 3.5% fuel oil, when detonated, produces fumes having acontent of nitrogen dioxide approximately 15 times greater than thefumes of conventional explosives, such as nitroglycerine baseexplosives. Moreover, the concentration of nitrogen dioxide exceeds thelethal limit of 0.025%. Using fuel oil in amount greater than 6% reducesthe sensitivity of the ammonium nitrate fuel oil mixture to detonation.Such mixtures containing 7.5% fuel oil gave 4 misfires or failures innine applications.

In this specification all percentages are on a weight basis unlessotherwise indicated or apparent.

Visual comparison of ammonium nitrate fuel oil mixtures containing 3.5%,5.7% and 7.5 of fuel oil does not reveal the difference in fuel oilconcentration. Such mixtures look alike; the differences therebetweenare almost imperceptible especially when ammonium nitrate prills withhigh absorption power for fuel oil are used. Accordingly, the appearanceof the mixture does not reveal whether the mixture has been properlyproportioned, or whether an error has been made in the fuel oil content.Such error in the proportionment of the mixture can readily occur whenweighing out the ammonium nitrate or the fuel oil or due to inadequatefunctioning of the mixers or of the feeders of these materials tocontinuous mixers with consequent change in the composition of themixture producing mixtures with less or more of fuel oil than thedesired range of from 5.5% to 6%.

The report of investigations 6015 of the US. Bureau of Mines referringto the fire and explosion in the ANFO-mixing building in Norton,Virginia, that occurred on December 27, 1961, shows that in this mixingplant there did not exist any process or apparatus to check theuniformity of the mixing or the content of the fuel oil in the ANFO.This report is of particular interest because other plants are operatedunder iden- The mixing of ammonium nitrate fuel oil in itself is alreadya dangerous operation, if executed without usual precautions observed bythe explosive manufacturers, but the lack of control of the uniformityof the ANFO, or of its fuel oil content, is still more dangerous,because the fumes produced by the detonation of ANFO with low fuel oilcontent may affect the life and the health of an unlimited number ofminers in underground blasting operations. It is a principal object ofthe present invention to provide a method of controlling theproportionment of ammonium nitrate and fuel oil to insure mixturethereof in such proportions that when detonated the gaseous productsproduced are of low toxicity, i.e., contain appreciably less than theamount of nitrogen dioxide toxic to humans.

It is another object of this invention to provide a process forcontrolling the mixing of ammonium nitrate with fuel oil which rendersit immediately apparent when any error has occurred in the amount offuel oil used and without requiring the use of complicated physical orchemical analysis to determine the fuel oil content or the relativeproportions of the constituents of the mix.

Other objects and advantages of this invention'will be apparent from thefollowing detailed description thereof.

In accordance with this invention a new, safe and simple procedure isprovided involving coloring the ammonium nitrate with a dyestuffdissolved in the fuel oil. Any dyestulf which can be readily dissolvedin the fuel oil, which dyestuff is chemically inert with respect to theammonium nitrate and which imparts a distinctive color to the ammoniumnitrate fuel oil mixture such as to enable ready differentiation betweenthe colored ammonium nitrate fuel oil mixture and such admixture madewith uncolored fuel oil, can be used. The amount of dyestuff thusemployed is the amount required to impart a distinctive color to the mixand hence will vary with different dyestuffs. In general the use ofabout 0.05% to 0.5% dyestuff based on the weight of fuel oil will befound adequate. It is important that the dyestuff used be soluble in thefuel oil; unless the dyestuff is dissolved in the fuel oil, and thuseach particle of fuel oil is dyed to the same extent, so that therelative distribution of the dyed fuel oil throughout the ammoniumnitrate is readily apparent upon visual inspection, the advantageshereinafter pointed out are not obtained.

In accordance with one aspect of this invention, the admixture of theammonium nitrate with the fuel oil containing the dissolved dyestuffenables ready and prompt ascertainment of whether or not the fuel oil issubstantially homogeneously dispersed throughout the ammonium nitrate.Should the fuel oil be concentrated in greater amounts in certainportions of the ammonium nitrate than others, this will be readilyapparent from the difference in color of those portions containingdifferent amounts of the colored fuel oil. By having the fuel oiluniformly and homogeneously distributed throughout the ammonium nitrate,the resultant mixture when detonated will not contain in any portionsthereof relatively small amounts of fuel oil below about 5.5 which smallamounts cause the formation of fumes containing dangerous or highlytoxic amounts of nitrogen dioxide.

In accordance with another aspect of this invention, for any givendyestuff employed with the fuel oil a small reference sample is preparedcontaining the dyed fuel oil and the ammonium nitrate in the properportions, namely, from 94.0% to 94.5% ammonium nitrate and 5.5 to 6%fuel oil. This reference sample is used as the standard or comparisonsample. By comparing the color of the mixture produced by batch orcontinuous mixing of ammonium nitrate and the dyed fuel oil with thecolor of the reference sample containing of course the same dyestuff inthe same relative amounts, one can tell immediately whether or not theproportions of the ammonium nitrate and fuel oil are correct.

Moreover, the present invention discloses readily whether thedistribution of the fuel oil and the ammonium nitrate is uniform, i.e.,whether the fuel oil is uniformly distributed throughout the ammoniumnitrate. A uniformly colored mix insures the presence of a uniformmxiture. On the other hand, a heterogeneous mixture in which the fueloil is not uniformly distributed throughout the ammonium nitrate isimmediately apparent by the splotchy or different colored appearance.

The following examples are given for illustrative purposes. It will beunderstood the invention is not limited to these examples.

In the examples readily available, commercial dyestuffs were usedtheYellow Sudan 3G, Color Index 2822, reference No. 12700; the Black SudanBB, Color Index 2899, reference No. 26,150. The Grease Red BB, referenceNo. 26,125, as well as the other two dyestufits are commerciallyavailable oil-soluble organic dyestuffs chosen for exemplary purposes.As indicated, other dyestuffs soluble in the fuel oil and which impartcharacteristic color thereto chemically inert to the ammonium nitratecan be used.

EXAMPLE I 11.4 kg. of fuel oil #2 colored with 4.7 grams of Yellow Sudan3G per liter dissolved in the fuel oil were mixed with 188.6 kg. ofammonium nitrate in prills of 2 4 mm., coated with an organic anticakingproduct. The mixer used was a kneader with two horizontal blades,rotating in opposite directions and the mixing was stopped when theprills had reached a uniform coloration.

A sample of this colored mix of ammonium nitrate and 4 fuel oil was usedas a reference sample and additional mixes prepared employing thereference sample as the standard, which different mixes were in everycase compared with the standard to obtain substantially the same color.Chemical analysis of the different mixes thus prepared showed that thefuel oil content varied from 5.64% to 5.83%. The concentration of fueloil in the reference sample and that considered the theoretical optimumis 5.7%. This demonstrates the efficiency of the process to obtainproper proportionment of the ammonium nitrate and the fuel oil.

EXAMPLE II 188 kg. of ammonium nitrate, fertilizer grade, were mixedwith 12 kg. of fuel oil #2, colored with 0.5 gram of Black Sudan BB perliter dissolved in the fuel oil, in a double motion paddle mixer. Whenthe coloration appeared uniform, the mixing process was stopped.

Samples of the uniformly colored mixture were taken and analyzed todetermine their fuel oil content. Analysis showed a variation of from5.87% to 6.16%, demonstrating that the uniformity of the color of themixture employing the dyed fuel oil is an accurate indication of thehomogeneous character of the mixture.

Comparative Example III A mixture of ammonium nitrate with fuel oilcontaining 5.7% fuel oil colored with Grease Red BB dissolved in thefuel oil in amount of 0.7 gram of this dyestuff per liter was producedfollowing the procedure of Example I.

For comparative purposes a second mixture was produced by mixing 192 kg.of crystalline ammonium nitrate with 8 kg. of fuel oil colored with 0.7gram of Grease Red 5B per liter using the same procedure. Thiscomparative mixture contained only 4% fuel oil. Visual inspection ofboth mixtures showed immediately the lack of fuel oil in the comparativemixture.

Comparative Example IV 184 kg. of ammonium nitrate of equal quality asthat used in Example I were mixed with .16 kg. of fuel oil colored with4.7 grams of Yellow Sudan 3G per liter dissolved in the fuel oil, in amixer described in Example H. Comparing the coloration intensity of themixture, which intentionally contained 8% fuel oil, to a control mixturewith a 5.7% fuel oil content, colored with the same dyestuff, the excessof fuel oil was immediately noticed. Observing the two mixtures througha moncromatic filter of 4,700 Angstrom, the difference was even morepronounced.

EXAMPLE V 'Into a mixer provided with a horizontal blade stirrer isintroduced from one side, the ammonium nitrate and fuel oil dyestuffsolutions containing 0.7 gram Grease Red BB per 'liter, by means offeeders which maintain the weigth ratio of 94% ammonium nitrate to 6%colored fuel oil. The horizontal blade stirrer mixes the two ingredientsand at the same time pushes them from the entrance side to the otherside of the mixer, where the finished mixture is discharged by anendless screw, to be packed. A conventional colorimeter is employed atthe discharge side of the mixer sensitive to the color of the mixture.This colorimeter is adjusted for a predetermined color of the mixdetermined by the dyestuff used and the resultant color of the mixturecontaining proper proportions of about 94.0% to 94.5% ammonium nitrateand 5.5% to 6% fuel oil. Any appreciable deviation from this colorcauses the colorimeter to energize an alarm signal, so that the operatorcan stop the mixing process and make the necessary adjustment to producea mix having the proper proportions.

The above examples are exemplary only and the in vention is not confinedthereto but includes modifications such as the use of dyestuffs otherthan those mentioned, and use of dyestuffs in different concentrationsto produce colored fuel oils in which the dyestuff is dissolved in thefuel oil. The ammonium nitrate fuel oil mix can contain, in addition tothe dyestulf dissolved in the fuel oil, other additives commonly used inthe manufacture of explosives.

The expression petroleum oils is used herein in a broad sense to includepetroleum liquids such as fuel oil, petroleum distillates and liquidpetroleum residues, including asphalts.

It will be understood the invention is not limited to the disclosuresherein, except as indicated by the appended claims. I

What is claimed is:

1. A process of producing detonable mixtures of ammonium nitrate andpetroleum oils in regulated proportions such that when detonated thefumes produced are of low toxicity, which process comprises mixing withthe petroleum oil a control oil-soluble dyestuif to produce a coloredpetroleum oil of a definite color, mixing the thus colored petroleum oilcontaining oil-soluble dyestuff with ammonium nitrate to uniformlydistribute the colored petroleum oil throughout the ammonium nitrate andproduce a control sample having a predetermined color substantially thesame as the color of the desired mixture of ammonium nitrate andpetroleum oil in proportions such that when this mixture is detonatedfumes of low toxicity are produced, mixing ammonium nitrate with coloredpetroleum :oil having the same dyestuff and in the same relativeproportions as in the colored petroleum oil employed to proluce saidcontrol sample, and regulating such mixing in accordance with the colorof the control sample to produce mixtures of ammonium nitrate andcolored petroleum oil in which the colored petroleum oil is uniformlydistributed throughout the ammonium nitrate and the mixtures havesubstantially the same color as the color of the control sample, andwhich mixtures upon detonation result in a gaseous atmosphere of lowtoxicity.

2. The process as defined in claim 1, in which the petroleum oil is afuel oil and the ammonium nitrate and colored fuel oil in both thecontrol sample and the desired product are mixed in proportions of from94.0% to 94.5% by weight of ammonium nitrate and from 5.5% to 6% byweight of fuel oil, the color of the control sample being substantiallymatched by that of the desired mixture to insure that the amount of fueloil incorporated therein is within the said range of 5.5 to 6%.

3. The process of producing detonable mixtures of ammonium nitrate fueloil as defined in claim 2, in which the color of the mixture produced bymixing the ammonium nitrate and colored fuel oil is measured by acolorirneter which when the mixture deviates in color from that of thecontrol sample energizes a signal to indicate the deviation from thepredetermined color, which signal is employed to control the mixing ofthe ammonium nitrate and colored fuel oil to produce a mix havingproportions of fuel oil and ammonium nitrate within the range of from94.0% to 94.5% by weight of ammonium nitrate and from 5.5 to 6% byweight of fuel oil, with the fuel oil substantially homogeneouslydistributed throughout the ammonium nitrate.

4. The process of producing detonable mixtures of ammonium nitrate andpetroleum oil in regulated proportions such that when detonated, thefumes produced are of low toxicity, which process comprises utilizing acolored petroleum oil made by mixing petroleum oil with an oil-solubledyestuff, mixing the thus colored petroleum oil containing oil-solubledyestulf with ammonium nitrate to uniformly distribute the coloredpetroleum oil throughout the ammonium nitrate and produce a controlsample having a predetermined color substantially the same as the colorof the desired mixture of ammonium nitrate and petroleum oil inproportions such that when this mixture is detonated fumes of lowtoxicity are produced, mixing ammonium nitrate with colored petroleumoil having the same dyestuff and in the same relative proportions as inthe colored petroleum oil employed to produce said control sample, andregulating such mixing in accordance with the color of the controlsample to produce mixtures of ammonium nitrate and colored petroleum oilin which the colored petroleum oil is uniformly distributed throughoutthe ammonium nitrate and the mixtures have substantially the same coloras the color of the control sample, and which mixtures upon detonationresult in a gaseous atmosphere of low toxicity.

References Cited in the file of this patent UNITED STATES PATENTS OrelupDec. 9, 1941 Karner Nov. 12, 1946 OTHER REFERENCES

1. A PROCESS OF PRODUCING DETONABLE MIXTURES OF AMMONIUM NITRATE ANDPETROLEUM OILS IN REGULATED PROPORTIONS SUCH THAT WHEN DETONATED THEFUMES PRODUCED ARE OF LOW TOXICITY, WHICH PROCESS COMPRISES MIXING WITHTHE PETROLEUM OIL A CONTROL OIL-SOLUBLE DYESTUFF TO PRODUCE A COLOREDPETROLEUM OIL OF A DEFINITE COLOR, MIXING THE THUS COLORED PETROLEUM OILCONTAINING OIL-SOLUBLE DYESTUFF WITH AMMONIUM NITRATE TO UNIFORMLYDISTRIBUTE THE COLORED PETROLEUM OIL THROUGHOUT THE AMMONIUM NITRATE ANDPRODUCE A CONTROL SAMPLE HAVING A PREDETERMINED COLOR SUBSTANTIALLY THESAME AS THE COLOR OF THE DESIRED MIXTURE OF AMMONIUM NITRATE ANDPETROLEUM OIL IN PROPORTIONS SUCH THAT WHEN THIS MIXTURE IS DETONATEDFUMES OF LOW TOXICITY ARE PRODUCED, MIXING AMMONIUM NITRAE WITH COLOREDPETROLEUM OIL HAVING THE SAME DYESTUFF AND IN THE SAME RELATIVEPROPORTIONS AS IN THE COLORED PETROLEUM OIL EMPLOYED TO PROLUCE SAIDCONTROL SAMPLE, AND REGULATING SUCH MIXING IN ACCORDANCE WITH THE COLOROF THE CONTROL SAMPLE TO PRODUCE MIXTURES OF AMMONIUM NITRATE ANDCOLORED PETROLEUM OIL IN WHICH THE COLORED PETROLEUM OIL IS UNIFORMLYDISTRIBUTED THROUGHOUT THE AMMONIUM NITRATE AND THE MIXTURES HAVESUBSTANTIALLY THE SAME COLOR AS THE COLOR OF THE CONTROL SAMPLE, ANDWHICH MIXTURES UPON DETONATIONI RESULT IN A GASEOUS ATMOSPHERE OF LOWTOXICITY.